This project will investigate whether prepaid group practice enrollees have lower utilization rates than conventional insurance enrollees. PGPs as a combination of insurance firms and medical provider, have the incentive to keep down medical care costs. Other medical providers that deal with conventional insurance enrollees have less of this incentive. The project will also investigate the effect of PGP market share on the utilization rates of conventional insurance enrollees. To estimate utilization rates correcting for self-selection, a two-stage techniques will be used. In the first stage the probability of joining a PGP is estimated with probit analysis. In the second stage utilization (e.g. physician visits) is regressed on its determinants plus a correction factor calculated from the first stage results. The estimator is consistent. The data source is the National Medical Care Utilization and Expenditure Survey.